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The photosensitizer should be selectively incorporated into and accumulated in the neoplastic cells for a sufficiently prolonged period of time. In the series of Stylli et al. [16] the magnitude of photosensitizer uptake was directly associated with patient survival after PDT. In overall, concentrations of the various photosensitizers in gliomas are reported to be 4- to 300-fold higher than those in normal brain [6], and are greater in glioblastoma multiforme (GBM) than in anaplastic astrocytoma (AA), and in recurrent neoplasms compared to newly diagnosed ones. Under such conditions PDT can be selectively applied to the tumor with preservation of the adjacent tissues. Obviously, the agent should not cause major systemic toxicity.

Currently, only a few photosensitizers suitable for clinical application are available on the market. The list of the most studied include Foscan^® (m-temoporfin), Photofrin^® (porfimer sodium), Laserphyrin^® (talaporfin sodium), and 5-aminolevulinic acid (5-ALA) [2]. The latter is currently widely used for intraoperative real-time visualization of malignant gliomas and their differentiation from perilesional brain, and has resulted in dramatic improvement of the total tumor resection rate (roughly from 40 to 80%) [6, 10, 17, 18]. However, application of 5-ALA for PDT is considered to be of limited efficacy [7], yet some very promising data have been reported [19, 20].